Revising The Protocols to Ensure Reliability, Cost Effectiveness and High Sample Throughput for Water Stable Isotope Analyses In Continuous Flow Mode using the Gasbench II.
Abhayanand Singh Maurya1, Rajendra Dattataryi Deshpande2, Miral Shah3, Sushil Kumar Gupta4
1Abhayanand Singh Maurya, Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee (Uttarakhand), India.
2Rajendra Dattataryi Deshpande, Physical Research Laboratory, Navrangpura, Ahmedabad, Gujarat, India.
3Miral Shah,  Laboratoire de Glaciologie et Géophysique de l’Environnement  Saint Martin d’Hères Cedex, France.
4Sushil Kumar Gupta,  Physical Research Laboratory, Navrangpura, Ahmedabad, Gujarat, India.
Manuscript received on November 16, 2014. | Revised Manuscript received on December 21, 2014. | Manuscript published on December 30, 2014. PP: 222-227  | Volume-4 Issue-2, December 2014.  | Retrieval Number:  B3669124214/2013©BEIESP

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Abstract: The continuous flow isotope ratio mass spectrometer (CF-IRMS) coupled with automated sample preparation device Gasbench II and equilibration system measures oxygen and hydrogen isotope ratios with typical external precision of around ±0.1 ‰ for  18O and ±1 ‰ for D, although internal analytical precision is better than 0.06 ‰ for oxygen and 0.5 ‰ for hydrogen. In CF-IRMS method, an aliquot of the gas (CO2 /H2 + Helium), equilibrated with water sample, is transferred from the head-space of the exetainer into the massspectrometer for isotope ratio measurement. The observed difference between external and internal precision is governed by the operating procedures that influence the online chemistry for equilibration and transfer of the gas in to IRMS. These procedures also govern the sample throughput and long term stability of the machine. With a view to minimize the difference between external and internal precision and to maximize the throughput with high reliability at minimum cost experiments were undertaken. The experiments investigated: (i) optimum duration of equilibration for oxygen analyses, (ii) modes for manual introduction of water sample in the exetainer i.e. before or after flush-filling with equilibrating gas, (iii) effects of the difference between room temperature and sample tray temperature, (iv) effects of septum reuse, and (v) reuse of platinum rod on long term basis. In addition, important maintenance related issue pertaining to analytical needle for the injection and flushing is addressed. The experiments achieved external precision better than 0.07 ‰ for  18O and 0.8 ‰ for D with large sample throughput and long term stability using 300l of water sample. Other optimized parameters for oxygen are; equilibration duration of 16 hrs at 32ºC, 540 seconds of flushing duration and introduction of water sample after flush-filling. The parameters for hydrogen are 45 minutes and 320 seconds after flush-filling.
Keywords: Water Stable Isotope, Protocols, Flush filling, Maintenance.